1. Field of the Invention
The present invention relates generally to an industrial workcell system and method, and, more particularly, to an all-electric industrial workcell using no plant-provided facilities suitably adapted for use in resistance welding operations.
2. Discussion of the Prior Art
An industrial or manufacturing workcell is generally provided in a plant or factory for performing various processing tasks on or to material or workpiece conveyed to the workcell. Exemplary industrial operations include welding (including resistance welding), piercing, mechanical fastening (e.g., riveting), forming operations, machining operations, material handling operations, assembly operations, hemming operations, adhesive application operations, and cutting operations (e.g., by way of laser systems). A key attribute associated with such a workcell is, of course, performance. However, since there are generally many different ways in which to implement any particular industrial operation, distinguishing key factors often also include cost (including start-up and maintenance), maintainability of the cell (e.g., availability/adaptability of replacement parts), and up time (alternately referred to as "down time"). Furthermore, industrial workcells generally include a variety of processing equipment from a variety of vendors, thus making inter-operability an issue. In particular, for large manufacturing concerns (e.g., an automotive manufacturer), the design and implementation of such industrial workcells are often delegated to "systems integrators," who take the manufacturers basic workcell specification, and then design, build, and test the workcells. The verified workcells are then torn-down, transported, and rebuilt at the large concerns' manufacturing site. In an increasingly competitive marketplace, investigation into improving industrial workcells to meet key attributes, such as performance, cost, maintainability, and down time, has been, generally, on a piece meal (i.e., individual component or subassembly) basis. Accordingly, the prior art has not seen significant and substantial improvements vis a vis the above-mentioned attributes.
To provide a more concrete idea of the direction taken and resulting shortcomings of the prior art, reference is now made to FIG. 1. FIG. 1 shows a prior art industrial workcell 10 adapted for industrial resistance welding operations. Workcell 10 includes a station panel view 12, a power and interface panel (PIP) 14, a robot controller 16, a robot 20 associated with robot controller 16, a welding transformer 22, a plant-provided compressed air manifold 24, a plant-provided cooling water feed manifold 26, a plant-provided cooling water return manifold 28, an air cylinder 30 mounted on a wrist of robot 20, a welding gun 32 coupled with air cylinder 30, and a welding current cable 34 coupling the welding gun 32 to a secondary side of transformer 22. Workcell 10 further includes a clamping tool 36, including a plurality of compressed air-actuated clamps 37 for securing the workpieces to be welded together in a predetermined fixed relationship with each other and relative to the fixed base.
FIG. 2 shows a generally enlarged view of the portion of FIG. 1 enclosed by dashed lines. In particular, note the large number of compressed air hoses 38, and cooling water feed and return hoses 39. It should be appreciated by those skilled in the art that the compressed air is provided for actuating air cylinder 30 to operate welding gun 32 (i.e., close and apply clamping force), and air clamps 37, while cooling water provided by manifolds 26 and 28 is provided for cooling power switching devices in weld control 18 (e.g., silicon controlled rectifiers--SCR), transformer 22, secondary (high current) cable 34, and welding gun 32, particularly the welding electrodes or tips included thereon.
There are a host of shortcomings associated with workcell 10. Foremost perhaps is the unreliability, or, in other words, the "down time" exhibited by such a configuration. It has been observed that over 80% of the down time of a workcell of the type shown in FIG. 2 can be attributed to the host of air hoses 38, and feed and return cooling water hoses 39. The necessity for such hoses, of course, derives from the use of conventional air cylinders/cooling designs, which rely exclusively on plant-provided facilities. The material costs of the various hoses, pipes, valves, etc. is tremendous. Furthermore, the labor costs for configuring robot 20 with the various hoses 38, 39, and the associated pipes, valves, etc. (i.e., "dressing" the robot), due to the employment of various skilled trades (such as pipefitters, plumbers, etc.), is likewise tremendous. Further, it should be particularly apparent that the "build" time is significantly increased, thus causing an increase in the delivery time of such a workcell to the commissioning manufacturer. Support hardware required for use of plant-provided cooling water, and compressed air, such as a surge tank and dense pack (i.e., required for control of the air cylinders), further escalate the material cost of workcell 10.
Another cost associated with workcell 10 relates to its uniqueness vis a vis other similarly-configured workcells in a plant environment. It should be appreciated that each workcell, necessarily, is a unique configuration, due to the fact that each length of hose, each bend in a pipe or conduit, and each selected placement for various cooling water fittings is necessarily tailored to the particular workcell. It should be further appreciated that the kinematics of the host of hoses (pejoratively referred to as "spaghetti") cannot be accurately predicted or modelled. Accordingly, the robot movements in each workcell must be inputted on-site, step-by-step, to ensure that hoses do not become entangled. To further exacerbate this problem, the resulting "windows" in which a robot arm may move through in order to reach, for example, a weld point, is significantly reduced, due, again, to the proliferation of the compressed air and water hoses 38, 39. In a manufacturing plant having a large number of workcells, the aggregate cost in having to individually configure each workcell is staggering.
It should be appreciated, however, that the shortcomings of prior art workcell 10 do not relate solely to cost, maintainability, and reliability, but rather, also extend to the performance of workcell 10. For example, reduced "window" openings restrict path choices for robot arm entry to the workpiece, thus increasing the time to process the workpiece. Further, the use of air cylinders, such as cylinder 30, restrict the jaw opening choices for weld gun 32. In particular, use of an air cylinder generally provides either open/close operation, or wide open/intermediate open/closed operation. Thus, as shown in FIG. 2, the conventional configuration may only provide for two jaw openings having opening widths of A and B. This inflexibility leads to increased processing time. For example, to clear an obstruction that is only slightly greater than distance A, when moving from one weld point to the next weld point, the jaw opening of gun 32 must be opened to its wide open position, tip separation distance B. It should be apparent that this inflexibility manifests itself in an increased processed time, as extra time is needed to both open the jaw to the wide open position, and then to close the jaw upon arrival at the next weld spot to its closed positioned. Moreover, performance as it relates to weld quality if also unsatisfactory in workcell 10. Particularly, a clamping force applied by gun 32 is an important factor in producing a quality weld on a statistically consistent basis. Due to limitations in the input compressed air pressure, the crude pressure regulation by the dense pack, and other factors (e.g., pressure drops in hose runs), clamping force cannot be controlled very accurately. The upshot of this inherent limitation regarding clamping force is that destructive-testing must be performed to verify welding operations from time-to-time (i.e., welded workpieces must be physically torn apart to determine, for example, break-away force, and weld nugget quality). Finally, each air clamp 37 requires an individual I/O port, thus increasing the interface size, and the associated wiring requirements. The compressed air-actuated air clamps 37 cannot be linked, as by some type of bus architecture (e.g., manufacturing automation protocol--MAP) since the associated control valves and the like are not amenable to such control.
Of course, many of these shortcomings are not limited to an industrial resistance welding operation; for example, a piercing operation relies on plant-provided hydraulics. Accordingly, such an industrial process also requires the above-described host of connecting hoses/valves and the problems associated therewith.
Accordingly, there is a need to provide an improved industrial workcell to process a workpiece or workpieces, such as a workcell adapted for a resistance welding operation, that minimizes or eliminates one or more of the problems as set forth above.